The Giants held their first post-training camp practice yesterday at their team facility and it was surprising not to see Will Beatty on the field manning the left tackle position. After all, it appeared as if Beatty had left his back problems behind at the University at Albany. After missing practice time and the first preseason game he was able to return to work and said he was feeling better.

That’s not the case any more.

“He’s back on the shelf,’’ coach Tom Coughlin said after practice, not sounding pleased. “He’s back in the training room.’’

Asked when Beatty might return, Coughlin said “I have no idea.’’

This is a major step backward for the Giants, who need Beatty to be healthy and on the field in order to prevent the offensive line puzzle from becoming jumbled. Beatty missed the last six regular-season games and the entire playoff run last season because of a detached retina. In the spring, working too strenuously in the weight room, he hurt his back and sciatic nerve. Beatty could not participate in practice at the start of camp, but found his way onto the field the last few days of practice in Albany. A return home brought a return of his back ailment.

“They evaluated him last night and they felt like if he kept on going the way he is right now he would have only gotten worse and worse,’’ Coughlin said. “They shut him down.’’

Without Beatty, the Giants are going with 31-year old veteran Sean Locklear, a player not considered a long-term answer if Beatty is out for an extended period of time. There is no promising option on the bench, and the best move would likely be to shift David Diehl back to left tackle, where he started for the Giants’ last two Super Bowl teams. Diehl was moved to right tackle this summer to replace retired Kareem McKenzie. If Diehl moved back to the left side, the replacement at right tackle would probably be Locklear or second-year James Brewer.